I suppose it's the inevitable result of social media taking over the internet and fandom with it: the visual is more interesting than the verbal. This is how people interact online these days, and it's hardly surprising that it's impacting fandom both as the old guard change our ways, and the new people coming in grew up on an internet that is wildly different from what ours used to be. Tumblr was designed to be visual, and fandom somehow manhandled it into being semi-functional for verbal exchanges - but yeah, far from ideas, compared to forums or old-styled journals. And I'm frankly kind of vary about posting anything that can be controversial over there, since I have already had posts passed around as bad takes they were never meant as :/

I haven't followed tumblr's history too closely, but my impression has always been that it's a bit of a problem child in that it is wildly popular but also difficult to turn a profit from exactly because it was designed for content that demands a lot of server space, and for a generation that is alien to the concept of paying money to publish their content.